Field of the Invention
The present disclosure relates to a method for cleaning a liquid ejecting head.
Description of the Related Art
A liquid ejection head that ejects a liquid using a heat generating resistive element is used in a liquid ejecting apparatus, such as an inkjet printer. This liquid ejection head is provided with a flow path forming member that forms a flow path of a liquid, such as ink, and a heat generating resistive element. The heat generating resistive element is formed by, for example, an electrothermal converting element. When the heat generating resistive element is made to generate heat, a liquid is heated suddenly and is made to foam in a liquid contact area (i.e., at a thermal action portion) located above the heat generating resistive element. The foaming causes pressure with which the liquid is ejected from an ejection port. An image is recorded on a surface of a recording medium, such as paper, with the liquid. A configuration in which the heat generating resistive element is covered with an insulating layer to insulate the heat generating resistive element from the liquid is proposed. The heat generating resistive element receives the following complex actions: physical actions including impact due to cavitation caused by foaming and deaeration of the liquid, and chemical actions caused by the liquid. Thus, a configuration in which the heat generating resistive element is covered with a protective layer for protection is proposed.
In a liquid ejection head, the following phenomenon may occur: an additive, such as a coloring material included in a liquid, is decomposed when heated at a high temperature; the additive changes to a highly insoluble substance; and the additive is physically adsorbed into a layer that touches the liquid, such as an insulating layer and a protective layer. The physically adsorbed object is called “kogation.” When kogation adheres to the protective layer, uneven heat conduction from a thermal action portion to the liquid may occur, foaming may become unstable, and ejection characteristics of the liquid may be affected.
To address this problem, Japanese Patent Laid-Open No. 2008-105364 discloses a configuration in which an electrically connectable upper protective layer is disposed in an area including a thermal action portion to form an electrode that causes electrochemical reaction with a liquid. There is a cleaning method in which kogation on the thermal action portion is removed by causing an upper protective layer to be eluted by an electrochemical reaction. In this method using the electrochemical reaction with the liquid, air bubbles are generated when the liquid is decomposed while the upper protective layer is eluted. Since the air bubbles stay on the upper protective layer, there is a problem that the electrochemical reaction between the upper protective layer and the liquid is inhibited. To address this problem, in Japanese Patent Laid-Open No. 2008-105364, cleaning is performed while pushing out the generated air bubbles from a foaming chamber by sucking the liquid or pressurizing from the side of a liquid supply port so that inhibition of the electrochemical reaction is prevented.